Electrochemical behavior of Ni-W alloys obtained by magnetron sputtering

Nanocrystalline Ni-W coatings with a range of compositions from pure nickel to pure W were obtained by magnetron sputtering. A multiscale analysis was conducted to characterize the microstructure of the deposits. Their electrochemical behavior in acidic medium was studied using polarization curves and Electrochemical Impedance Spectroscopy. The Ni-W coatings were of similar grain size, roughness and crystallographic texture over a broad range of compositions, which enabled us to examine the role of W on the electrochemical behaviour. The results showed that W incorporation reduced corrosion at the open circuit potential, while for both the cathodic and the anodic domains, the electrochemical reactivity was amplified and reached a maximum value at a W content range of around 15-19 at.%. Although pure nickel and pure tungsten tend to passivate at anodic potential, Ni-W alloys form a mixture of non-protective corrosion products for this composition range.